In spite of significant efforts in academic and commercial laboratories, major breakthroughs in oral peptide and protein formulation have not been achieved. Relatively little progress has been made in reaching the target of safe and effective oral formulations for peptides and proteins. The major barriers to developing oral formulations for proteins and peptides include poor intrinsic permeability, lumenal and cellular enzymatic degradation, rapid clearance, and chemical stability in the gastrointestinal (GI) tract. Pharmaceutical approaches to address these barriers, which have been successful with traditional small, organic drug molecules, have not readily translated into effective peptide and protein formulations. Although the challenges are significant, the potential therapeutic benefits remain high especially in the field of diabetes treatment using insulin.
Scientists have explored various administration routes other than the injection for proteins and peptides. These routes include oral, intranasal, rectal, vaginal cavities for the effective delivery of large molecules. Out of the above four mentioned routes oral and nasal cavities have been of greatest interest to scientists. Both the oral and nasal membranes offer advantages over other routes of administration. For example, drugs administered through these membranes have a rapid onset of action, provide therapeutic plasma levels, avoid first pass effect of hepatic metabolism, and avoid exposure of the drug to hostile GI environment. Additional advantages include easy access to the membrane sites so that the drug can be applied, localized and removed easily. Further, there is a good potential for prolonged delivery of large molecules through these membranes.
The oral routes have received far more attention than has the other routes. The sublingual mucosa includes the membrane of ventral surface of the tongue and the floor of the mouth whereas the buccal mucosa constitutes the lining of the cheek. The sublingual mucosa is relatively permeable thus giving rapid absorption and acceptable bioavailability of many drugs. Further, the sublingual mucosa is convenient, acceptable and easily accessible. This route has been investigated clinically for the delivery of a substantial number of drugs.
The ability of molecules to permeate through the oral mucosa appears to be related to molecular size, lipid solubility and peptide protein ionization. Small molecules, less than 1000 daltons appear to cross mucosa rapidly. As molecular size increases, the permeability decreases rapidly. Lipid soluble compounds are more permeable than non-lipid soluble molecules. Maximum absorption occurs when molecules are un-ionized or neutral in electrical charges. Therefore charged molecules present the biggest challenges to absorption through the oral mucosae.
Most proteinic drug molecules are extremely large molecules with molecular weight exceeding 6000 daltons. These large molecules have very poor lipid solubility and are practically impermeable. Substances that facilitate the absorption or transport of large molecules (&gt;2000 daltons) across biological membranes are known as the enhancers, (Lee et al., Critical Reviews in Therapeutic drug Carrier Systems, 8, 91, 1991; Lee et al., Critical Reviews in Therapeutic drug Carrier Systems, 8, 115, 1991, 1992). Enhancers may be characterized as chelators, bile salts, fatty acids, synthetic hydrophillic and hydrophobic compounds, and biodegradable polymeric compounds.
Various mechanisms of action of enhancers have been proposed. These mechanisms of action, at least for protein and peptidic drugs include (1) reducing viscosity and/or elasticity of mucous layer, (2) facilitating transcellular transport by increasing the fluidity of the lipid bilayer of membranes, and (3) increasing the thermodynamic activity of drugs (Critical Rev, 117-125, 1991, 1992).
Many enhancers have been tested so far and some have found to be effective in facilitating mucosal administration of large molecule drugs. However, hardly any penetration enhancing products have reached the market place. Reasons for this include lack of a satisfactory safety profile respecting irritation, lowering of the barrier function, and impairment of the mucocilliary clearance protective mechanism. The main factor to be considered in the use of enhancers especially related to bile salts, and some protein solubilizing agents is extremely bitter and unpleasant taste. This makes their use almost impossible for human consumption on a daily basis. Several approaches were utilized to improve the taste of the bile salts based delivery systems, but none one of them are commercially acceptable for human consumption to date. Among the approaches utilized includes patch for buccal mucosa, bilayer tablets, controlled release tablets, use of protease inhibitors, buccally administered film patch devices, and various polymer matrices.
The basic problem associated with the above technologies is the use of large quantities of bile acids and their salts to promote the transport of the large molecules through membranes in the form of localized delivery system using patches or tablets. In spite of using protease inhibitors and polymer coatings the technologies failed to deliver proteinic drugs in the required therapeutic concentrations. Further, the problem is compounded because of the localized site effect of the patch which resulted in severe tissue damage in the mouth. Most attempts were made to deliver large molecules via the oral, nasal, rectal, and vaginal routes using single bile acids or enhancing agents in combination with protease inhibitors and biodegradable polymeric materials. However, it is extremely difficult to achieve therapeutic levels of proteinic drugs using these formulations. As single enhancing agents fails to loosen tight cellular junctions in the oral, nasal, rectal and vaginal cavities for a required period of time to allow passage of large molecules through the mucosal membranes without further degradation. This problem makes it impractical to use the above mentioned systems for a commercial purpose.
In order to overcome the above mentioned problem of the bitter taste, irritation and the penetration of large molecules through the sublingual, buccal and GI tract mucosal lining, a system has now been designed where protein drug was encapsulated in mixed micelles made up of combination of enhancers, e.g. yolk proteins (lecithins). This system allows opening of the paracellular junctions (tight junctions) in oral as well as in GI tract by gI motility movement with high degree of protease activity preserved and protecting molecules from premature degradation in the hostile acidic and proteolytic GI environment.
It is believed that the mixed micelles encapsulate molecules with high degree of efficiency (&gt;90% encapsulation). These mixed micelles are extremely small in the size (1 nm to 10 nm), and are smaller than the pores of the membranes in the oral cavity or the GI tract. It is therefore believed that the extremely small size of mixed micelles helps encapsulated molecules penetrate efficiently through the mucosal membranes of the oral cavity.
The absorption of proteins and peptides is believed to be enhanced by the diffusion of large molecules entrapped in the mixed micellar form through the aqueous pores and the cell structure perturbation of the tight paracellular junctions.
The amount of physiologically peptide or protein in the compositions of this invention is typically a quantity that provides an effective amount of the drug to produce the physiological activity (therapeutic plasma level) for which peptide or protein is being administered. In consideration of the fact that the bioavailability of any active substance can never be 100%, that is to say the administered dose of the active drug is not completely absorbed, it is preferable to incorporate slightly larger amount than the desired dosage. Where the dosage form is a spray (aerosol) or the like which is repeatedly dispensed from the same container, it is recommendably so arranged that the unit dose will be slightly greater than the desired dose. It should be understood that dosage should vary with species of warm blood animals such as man, domestic animals, and their body weights. Although the composition of this invention is prepared as the microfine droplets (1 to 10 nm or less) by the virtue of its preparation methods used and suitable combinations of enhancer compound characteristics. The utilization of atomizer or aerosol spray devices (metered dose inhalers or nebulizers) may be useful to further a sufficient reduction of particle size for effective inhalation from the nasal or oral cavity so the drug may successfully absorbed or reach to the specific site.
The therapeutic composition of the present invention can be stored at room temperature or at cold temperature. Storage of proteinic drugs is preferable at the cold temperature to prevent the degradation of the drugs and to extend their shelf life. While the mixed micellar therapeutic composition of the invention is applied to the mucosal membranes, the sites of administration may the same as those used for the usual mucosal therapeutic preparation. Generally, oral, transdermal and nasal are the favourite sites of the administration but the composition can be applied to the rectal and vaginal mucosa. According to the physiologically active peptide or protein used, the dosage form and the site of administration, a specific administration method can be selected.
As used herein, the term "edetate" is used herein to refer to pharmaceutically acceptable salts of ethylenediaminetetraacetic acid.